1. Field of the Invention
The present invention relates to an illuminating apparatus and a method of producing a lens sheet used therein.
2. Description of the Related Art
Conventionally, incandescent lamps or fluorescent lamps have been generally used as a light source for general illumination such as indoor lighting. However, in accordance with current technological advances in blue light-emitting diodes (LEDs), LEDs are now used as light sources for ceiling lights, down lights, and the like. See Japanese Patent Application Laid-Open No. 2007-220465.
FIG. 4 illustrates a so-called quasi-white-light source 100 which can be used as a light source for an illuminating apparatus. The quasi-white-light source 100 includes a lamp house 104 in which blue light-emitting LEDs, which serve as a plurality of light-emitting element chips 102a that constitute a light-emitting element 102, are arranged near each other on a bottom part, and a transparent resin 106 that seals a recessed part of the lamp house 104. In the transparent resin 106, yellow fluorescent bodies such as garnet (YAG) are dispersed as fluorescent bodies 108. Blue light that is emitted from the blue light-emitting LEDs 102a diffuses within the transparent resin 106 of the lamp house 104, and therein it is wavelength converted to yellow fluorescent light by the yellow fluorescent bodies 108 and emitted in this state to the outside of the lamp house 104 as emitted light L (L1, L2) indicated by dash-dot-dot lines for convenience. The portion indicated by reference numeral 103 in FIG. 4 is an electrode terminal.
The light L emitted from the quasi-white-light source 100 is deflected towards the necessary direction by passing through, for example, a lens sheet having a plurality of prisms that is disposed toward the front on an optical axis C of the quasi-white-light source 100, and thereby it functions as an illuminating apparatus.
However, light emitted from an illuminating apparatus using the quasi-white-light source 100 described above as a light source tends to exhibit slightly blue color in the center and slightly yellow color at the outer edges relative to the optical axis C of the quasi-white-light source 100. This is due to the following reason. In the emitted light indicated by L2 in FIG. 4 which travels along an optical path that is inclined relative to the optical axis C of the quasi-white-light source 100, the length of the optical path that passes through the transparent resin 106 in which the yellow fluorescent bodies 108 are dispersed is longer than the emitted light indicated by L1 in FIG. 4. The proportion of wavelength converted to yellow fluorescent light by the yellow fluorescent bodies 108 is thus larger compared to the emitted light indicated by L1. Here, L1 travels along an optical path that is parallel to the optical axis C of the quasi-white-light source 100.
Further, in light emitted from an illuminating apparatus using the quasi-white-light source 100, which has a plurality of blue light-emitting LEDs 102 arranged near each other as described above, as a light source, there are cases in which color unevenness called “chip appearance” occurs on the illuminated surface. This occurs because light with strong blue color and high brightness among the light emitted from the blue light-emitting LEDs 102a lines up together on the illuminated surface, and it is a phenomenon that is visually recognizable.
Thus, as a measure for overcoming the color unevenness mentioned above, there are cases in which a light diffusing part including a plurality of light scattering elements is provided on a surface opposite to the surface on which a plurality of prisms are formed of the lens sheet disposed on the optical axis C of the quasi-white-light source 100 (for example, refer to JP-A No. 2009-158473).
The light scattering elements can be fabricated comparatively easily by pressing an indenter to a surface of a mold matrix for injection molding a lens sheet (for example, refer to JP-A No. 11-53922). For example, when forming hemispherical light scattering elements on a lens sheet, as shown in FIG. 5, an indenter with a hemispherical tip is pressed to a surface of a mold matrix 120 for injection molding the lens sheet to form hemispherical recesses 122 utilizing the plastic deformation of the mold matrix 120. By injection molding a resin using the mold matrix 120 on which a plurality of the recesses 122 have been formed across a predetermined range, a lens sheet in which a plurality of hemispherical projections (light scattering elements) corresponding to the recesses 122 are formed across a predetermined range can be molded.
However, if the area density of the recesses 122 (area in which the recesses 122 are formed per unit area) is increased in order to achieve a greater light scattering effect by the light scattering elements of the lens sheet, when fabricating the plurality of recesses 122 by pressing the indenter to the mold matrix 120, the recesses 122 that are adjacent affect each other. In particular, the shape of recesses 122 which have already been fabricated is greatly distorted by the recesses 122 which are subsequently fabricated. Therefore, when providing the plurality of hemispherical recesses 122 in a lattice pattern at equal intervals horizontally and vertically, if the plurality of recesses 122 are fabricated in order by row or column units which constitute the lattice, the above-mentioned shape distortions become aligned in one direction and the shape distortions are reflected (transferred by injection molding) in the light scattering elements of the lens sheet. Thus, if such a lens sheet is used in an illuminating apparatus, the shape distortions aligned in one direction of the light scattering elements influence the light scattering effect by the light scattering elements and unidirectional anisotropy (or deviation of illuminated light) occurs in the light from the illuminating apparatus, and this provides negative influence to the rotational symmetry.
Further, in order to suppress the unidirectional anisotropy, a method has been proposed in which the plurality of recesses 122 are sequentially fabricated in a lattice-type spiral pattern originating from a recess 122x, which corresponds to the light scattering element positioned center of the lens sheet ((that is, on the optical axis C)), as shown by the dashed line arrows in FIG. 5.
However, even if the recesses 122 are fabricated according to this method, adjacent recesses 122 still affect each other, leading to the shape distortions described above, and shape anisotropy (four-fold rotational symmetry) appears in each of four regions divided by the two diagonal lines XX′ and YY′ shown in FIG. 5. In other words, excluding the recess 122x positioned center, the shapes of the recesses 122 on the two diagonal lines XX′ and YY′ are distorted due to the significant influence from three recesses 122 that are subsequently fabricated, whereas the shapes of the recesses that are not on the two diagonal lines XX′ and YY′ are distorted due to the significant influence from two recesses 122 that are subsequently fabricated. Further, the location (direction) which is influenced by the two recesses 122 that are subsequently fabricated is different in each of the four regions for the recesses 122 that are not on the two diagonal lines XX′ and YY′. Therefore, in the lens sheet molded from the mold matrix 120, anisotropy in each of the four regions occurs in the light scattering effect by the light scattering elements, and this may be visually recognizable as boundary lines or light/dark differences in the illuminated light.